Process of hardening steel



(No Model.)

F.- SEDGWICK. PROGB'SS OP HARDBNING STEEL.-

1\0.400,366. Patented Ma,1.26, 1889.

C .d e .07m m im. @j

UNITED STATES PATENT OEEICE.

FREDERICK SEDGW'IOK, OF OAK PARK, ILLINOIS.

PROCESS oF HARDENING STEL.

SPECIFICATION forming part of Letters Patent No. 400,366, dated March 26, i889. Application tiled July 7, 1888. Serial No: 279,292l (No modelz) To all whom t may concern,.-

Be it known that LFREDERICK SEDGWIGK, a citizen of the United States, residing in Oak Park, in the county of Cook and State of Illinois, have invented,a new and useful Improvement in the Process of IIardening Steel, of which the following is a specication.

In the hardening of bodies of steel for use in the arts, either as tools or as parts of machines, the metal is very apt to crack or check or spring ont of shape in the transition from heat to cold, owing to the fact that the center of the mass does not cool so rapidly as the surface, but continues to contract after the outer crust is iixed, thus causing a tendency by the center and ernst to tear asunder. Such cracking and springing are serions evils often, and the cases in which they do not occur are usually cases where the piece of metal is quite small in size. All qualities of steel are subject to them, and many pieces which seemingly have passed the ordeal of hardening without injury have, in fact, been ruined, and will manifest that fact when subjected to a slight concussion.

In practicing my invention, which is calculated to avoid the very serious evil above referred to, and also to improve the character of the hardened metal in other respects, I iirst heat the body or piece of steel to be treated in the usual manner, then immerse it in a cooling medium having some electrical conductivity, like water, and while thus immersed I subject it to the action of a current of electricity by connecting the metal or the tongs by which it is held to one pole and the bath to the other pole of a dynamo or other source of electrical energy.

The effects of the electric current which diffuses itself out of the metal being hardened into the cooling-bath are very marked. In the lirst place the mass seems to cool simultaneously from center to surface, so that the splitting and like imperfections are avoided. In the next place the treatment seems to prevent the formation of the large air-bubbles which customarily form on the surface of the metal while in the bath, thereby obviating the soft spots due tothe protection afforded by such bubbles against the cooling medium. In other words, the hardening is uniform and the entire mass is of an even quality; thirdly, the steel subjected to my process is less brittle than the ordinary hardened steel and very much tougher and stronger, and, lastly, the depth to which the crust is hardened is considerably greater than is usual.

The invention consists in subjecting the body or piece of metal to the action of a current of electricity while it is thus immersed in the cooling-bath.

In the accompanying drawing, which forms a part of this specification, I have shown an apparatus well adapted to the working of my improved process; but I do not wish to be limited thereto, as it can be greatly varied by those skilled in such matters without omitting or changing any essential of my process.

In said drawing, A represents a dynamo or other suitable source of electrical energy.

B is a vat or tank containinga cooling medium, O, having some ability to conduct electrical currents. IVater answers very well for this cooling medium.

In the bottom of the tank B is a copper plate, I), connected. to one pole of the dynamo by the post d and wire d.

E is a piece of heated steel ready to be plunged into the bath. It is held by the tongs F, and is connected to the other pole of the dynamo A by the wire f, leading from the tongs to the dynamo. It will now be seen that as soon as the steel, E, is pnt into the water the electrical circuit will be complete, and that the steel will then be affected by both the bath and the electricity.

The result of making the steel under treatment one of the electrical terminals in the manner stated is that the electric current diffuses itself throughout the entire body of metal and seeks egress therefrom in all directions, the water of the bath is decomposed, andthe gases thus formed pass off in minute bubbles from every portion of the surface of the steel. So rapid is the formation of these gas-bubbles that they crowd off any steambubbles which may tend to form on the steel, thereby obviating a very serious evil, as the steam-bubbles otherwise would adhere to the surface and cushion the chilling-fluid, and thus render the spot covered by them softer IOO than the adjacent parts. The action is also to deprive the center or core of the mass of its heat as Well as the surface, thereby rendering` the contraction of center and surface si- S multaneous.

I claim- The process of treating` steel herein set forth, the saine consisting in first heating the steel, then iinmersing it in a bath of coolingliquid, and simultaneously passing` an electric io current through it and the liquid, substantially as speciiied.

FREDERICK SEDGVVICK. Witnesses:

GEO., E. TITooMB, Fi W. JACKSON; 

